The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider with read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
However, the further miniaturization of the various components, particularly, the size and/or pitch of magnetic grains, presents its own set of challenges and obstacles in conventional products. Noise performance and spatial resolution are key parameters in magnetic recording media and are ongoing challenges to advance the achievable areal density of media. The dominant media noise source today is transition jitter. In sputtered media, it reflects the finite size, random positioning and dispersions in size, orientation and magnetic properties of the fine grains that comprise the media.
In order to address grain size and transition jitter it was proposed to change the recording mechanism from conventional magnetic field recording to heat assisted magnetic recording (HAMR), also known as “thermally assisted magnetic recording” TAR or TAMR. HAMR recording employs heat to lower the effective coercivity of a localized region on the magnetic media surface and write data within this heated region. The data state becomes stored, or “fixed,” upon cooling the media to ambient temperatures. HAMR techniques can be applied to longitudinal and/or perpendicular recording systems, although the highest density state of the art storage systems are more likely to be perpendicular recording systems. Heating of the media surface has been accomplished by a number of techniques such as focused laser beams or near field optical sources.
HAMR allows magnetic recording technology to use materials with substantially larger magnetic anisotropy (e.g., small thermally stable grains are possible) and coercive field by localized heating of the magnetic layer above its Curie temperature, where anisotropy is reduced. Currently the most promising media magnetic material for HAMR recording is chemically ordered FePt L10 alloy. Chemical ordering is achieved by deposition of FePt at elevated temperatures (450-700deg. C). However elevated deposition temperature of granular FePt films results in two main undesired effects: grain joining and grain roughening, which deteriorates microstructure of the films; and admixture of FePt with certain segregants, which deteriorates magnetic anisotropy and thus thermal stability of the grains. Therefore it is imperative to engineer segregant materials which allow for a columnar microstructure of FePt L10 with high magnetic anisotropy.
One example of a segregant for HAMR media which keeps FePt L10 grains isolated and yields high magnetic anisotropy is Carbon. However FePt—C granular media have generally spherical grains when formed, which undesirably limits the achievable thickness of the media for a given average grain diameter, thereby imposing a serious limitation on the signal strength of the media. These HAMR spherical grain FePt—C media are also rough, having a bimodal grain size distribution for larger grains (grain diameters from 6 nm to 8 nm) in addition to thermally unstable smaller grains (grain diameters less than 3 nm). Attempts to form more cylindrical or columnar grains for HAMR media suffer from their own shortcomings. Although some attempts have improved the grain shape from its spherical form, these attempts have consequently degraded the magnetic properties of the magnetic media dramatically. Even prior attempts at incorporating dual layers having oxide segregants have resulted in poor magnetic properties and are not useful for HAMR media. Such attempts compromise the magnetic properties of the media as a whole; in particular the coercivity is drastically diminished, thereby rendering the recording media effectively useless.